A so-called rotation sensor which is disposed to a rotating shaft, e.g., a steering shaft in a car to detect a rotation angle of a steering wheel integrated with the shaft is used (see, e.g., Patent Document 1 and Patent Document 2).
The rotation sensor disclosed in Patent Document 1 is a rotation sensor which measures a rotation angle of a main rotor which rotates in cooperation with two sub-rotors, the main rotor includes a gear, and each of the two sub-rotors also includes a gear. It is to be noted that the number of teeth of the gear in the main rotor is different from that of the gear in each of the sub-rotors, the gear in the main rotor meshes with the gear in one sub-rotor, and the gear in the main rotor meshes with the gear of the other sub-rotor. Further, each of the sub-rotors includes a magnet, and two AMR sensors which detect magnetic fluxes of the respective magnets are provided in a fixing portion of the rotation sensor.
Furthermore, an absolute rotation angle of the main rotor is calculated by utilizing, e.g., a phase difference between detection output values having different phases obtained from the two AMR sensors.
On the other hand, the rotation sensor disclosed in Patent Document 2 includes a rotor which is disposed to a rotating shaft and has a sensing portion whose width varies along a circumferential direction, and a fixed core which is disposed to a fixing member and arranged to face the sensing portion with a gap in an axial line of the shaft therebetween. It is to be noted that the fixed core has a first exciting coil through which an alternating excitation current flows to form a magnetic circuit between itself and the rotor and a first core which is formed of an insulating magnetic material to hold the first exciting coil. Moreover, this rotation sensor further includes a conductor layer whose width varies along a rotating direction and a Geneva gear which is fed at a predetermined rotation angle in accordance with each rotation of the rotor in one of the fixing members sandwiching a rotation surface of the rotor. Additionally, the rotation sensor also has a second exciting coil and a second core which holds this exciting coil, and includes a detection coil which gradually varies an output in accordance with a feed amount (the number of revolutions of the rotor) of the Geneva gear to detect the number of revolutions of the rotor.
Further, a displacement sensor which is disposed to a measurement target to detect a displacement amount of this measurement target is well known (see, e.g., Patent Document 3). The displacement sensor disclosed in Patent Document 3 includes a coil member in which a coil is formed by winding and to which an alternating current is applied and a mover which is arranged to face the coil member to form a predetermined gap therebetween and displaced along the coil. Furthermore, a displacement amount of the mover is detected based on an inductance fluctuation of the coil caused due to a change in an effective inductive coupling area between the coil and the mover.
Patent Document 1: Japanese Patent Application Laid-open No. 2001-505667 (pp. 6-10, FIG. 1)
Patent Document 2: Japanese Patent Application Laid-open No. 2003-202240 (pp. 2-4, FIG. 1)
Patent Document 3: Japanese Patent Application Laid-open No. 2004-170273 (pp. 5-7, FIG. 1)